Adaptation of the Steering Feel in Steer-By-Wire Steering Systems

ABSTRACT

The disclosure relates to a method for adapting the steering feel for a driver of a vehicle at an input element of the vehicle, wherein the vehicle has a steer-by-wire steering system, said method comprising the following steps: creating a reference of the steering feel and adapting the steering feel via scaling factors.

BACKGROUND INFORMATION

The present invention relates to a method for adapting the steering feel with the aid of an input element, for example, a steering wheel, for a driver of a vehicle, wherein the steering system is a steer-by-wire steering system.

Steering feel, in this case, is the combination of driving experience, that is, the steering torque at the steering wheel, the steering ratio, i.e., the ratio between the steering wheel and the steering angle, and the vehicle response, which reflects the feedback of the steering input via the vehicle to the driver.

Steering systems including a mechanical connection of the steering wheel to the steering angle are known in the related art. It is also known that steer-by-wire steering systems are possible, wherein there is no mechanical connection between the steering wheel and wheels to be steered.

SUMMARY OF THE INVENTION

Present EPS steering systems encompass a continuous mechanical coupling from the steering wheel of the relevant vehicle up to the steering angle. There is a mechanical push-through, which results in a ratio from the wheel up to the steering wheel, which is constant or not changeable with the aid of software. Therefore, an adaptation of the steering ratio, e.g., for a specific range, cannot be carried out. In contrast, there is no mechanical push-through in steer-by-wire steerings. Steer-by-wire steering systems are distinguished by the fact that there is no mechanical connection between the steering wheel and the steering angle of the steerable wheels. As a result, it is possible to move the steering wheel independently of the deflection or to change the ratio of the steerable wheel with respect to the input element depending on the range.

One object, therefore, is to provide a steering system for a steer-by-wire steering, wherein the steering feel of the driver at the steering wheel is adapted in order to impart an adequate or pleasant steering feel via the steering wheel.

As a first specific embodiment of the invention, a method is provided for adapting the steering feel for a driver of a vehicle at an input element of the vehicle, wherein the vehicle encompasses a steer-by-wire steering system, including the steps: creating a reference of the steering feel and adapting the steering feel with the aid of scaling factors.

Steer-by-wire steering systems offer the possibility to arbitrarily adjust the steering feel due to the steering wheel as a result of the decoupling of the input element, in particular the steering wheel, and the steering angle.

In particular, the steering feel can be adjusted in such a way that a high level of comfort and a high level of reliability results for the driver of the relevant vehicle.

As a second specific embodiment of the invention, a control unit of a steering system is provided, which includes a processing unit for carrying out a method as recited in one of claims 1 through 6.

As a third specific embodiment of the invention, a steering system is provided, which includes a control unit as recited in claim 7.

Exemplary specific embodiments are described in the dependent claims.

According to one exemplary specific embodiment of the invention, a method is provided, wherein the reference includes the elements: Basic steering torque having the input variables toothed bar force and vehicle speed and/or active return having the input variables steering wheel angle, driver torque, and vehicle speed and/or damping having the input variables steering wheel angular velocity, driver torque, and vehicle speed and/or hysteresis having the input variables steering wheel angular velocity, driver torque, and vehicle speed and/or inertia having the input variables steering wheel angular acceleration, driver torque, and vehicle speed.

The elements basic steering torque, active return, damping, hysteresis, and inertia are significant elements for creating a reference of a steering feel. There can be further elements, however, which can also be taken into account in the calculation of the reference.

According to one further exemplary embodiment of the present invention, a method is provided, wherein the scaling factors result as reference basic steering torque/instantaneous basic steering torque and/or reference active return/instantaneous active return and/or reference damping/instantaneous damping and/or reference hysteresis/instantaneous hysteresis and/or reference inertia/instantaneous inertia.

According to yet one further specific embodiment of the invention, a method is provided, wherein a setpoint steering feel results as:

Setpoint steering feel=basic steering torque·scaling factor_1+active return·scaling factor_2+damping·scaling factor_3+hysteresis·scaling factor_4+inertia·scaling factor_5.

In one further specific embodiment according to the invention, a method is provided, wherein the following results: Scaling factor_1=reference basic steering torque/instantaneous basic steering torque and/or scaling factor_2=reference active return/instantaneous active return and/or scaling factor_3=reference damping/instantaneous damping and/or scaling factor_4=reference hysteresis/instantaneous hysteresis and/or scaling factor_5=reference inertia/instantaneous inertia.

According to one further exemplary specific embodiment of the invention, a method is provided, wherein the input element is a steering wheel.

In one alternative specific embodiment, an input element is a joystick.

In one further specific embodiment according to the invention, a steering system is provided, wherein the steering system is a central controller or a single-wheel controller. A corner module, for example, can be considered as a single-wheel controller, in the case of which steering, brake application, and drive are integrated in one unit per wheel. Central controllers can differ, with respect to their configuration, from the single-wheel controller by the axially displaceable movement element, classically designed as a toothed bar.

According to yet one further specific embodiment of the invention, a steering system is provided, wherein the steering system is a central controller or a single-wheel controller.

As an idea of the invention, it can be considered to utilize the mechanical decoupling of the steering wheel from the steering angle of a vehicle in order to achieve an improved steering feel, in particular in order to allow for a steering motion of a steering wheel, which represents, for the relevant driver, a pleasant steering feel and an appropriate aid during the steering of the vehicle.

As a further idea of the invention, it can be considered to adapt the scaling of the steering feel, which results for the driver of a vehicle, in such a way that the steering feel also remains constant or its characteristics also remain constant in the case of different steering ratios.

In particular, the decoupling of the input element of the vehicle, in particular of the steering wheel, and of the steering angle in a steer-by-wire steering system of a central controller or a single-wheel controller is to be utilized in order to provide a scalability of the steering feel in the case of a change of the variable ratio of the steering system.

As a result, a reduction of the application effort advantageously results, since a limited number of application variants can be accessed. In addition, the utilization of a reference application is made possible, wherein the reference application is to be understood as a desired target application. Additionally or alternatively, one or multiple parameters can be introduced, which allow for an adaptation and scaling of the angle-dependent steering feel components via a ratio formation. As a result, an additional control option of the input element, in particular of the steering wheel, results.

The individual features can also be combined with one another, of course, whereby advantageous effects can also set in, in part, which go beyond the sum of the individual effects.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention become clear on the basis of the exemplary embodiments represented in the drawings. In the drawings

FIG. 1 shows a representation of the elements of a steering feel application device, and

FIG. 2 shows a flow chart of a sequence of a steering feel application according to the invention.

DETAILED DESCRIPTION OF EXEMPLARY SPECIFIC EMBODIMENTS

FIG. 1 shows a device for forming a steering feel for the driver of the relevant vehicle, wherein the device can be made up of different components. For example, including a first component 2, which provides a basic steering torque, a component 3, which applies an active return torque, whereby a desired setpoint return behavior of the steering wheel to the center results over the entire vehicle speed range. In addition, one component 4 can generate a damping, one further component 5 yields a hysteresis behavior, and one component 6 results in an inertia.

Input variables of the component basic steering torque 2 can be a toothed rod force and the vehicle speed. Input variables of the active return 3 can be the steering wheel angle, the driving torque, and the vehicle speed. With respect to the input variable of the instantaneous steering wheel angle, an appropriate setpoint return speed is predefined. This property determines the vehicle response and the return of the vehicle axle to the center. Therefore, in the case of ratios that are more direct than the reference ratio, there is a smaller steering wheel angle given the same wheel position and the return to the center must take place correspondingly more slowly. In the case of indirect ratios, the behavior is the other way around, so that the setpoint return speed must be increased in order to achieve a similar behavior as in the reference application of the steering feel. Input variables of the damping 4 can be the steering wheel angular velocity, the driving torque, and the vehicle speed. Input variables in the calculation of the hysteresis 5 can be the steering wheel angular velocity, the driving torque, and the vehicle speed. Input variables of the component 6 can be the steering wheel acceleration, the driving torque, and the vehicle speed.

A particular scaling factor can be calculated for the steering wheel angle variables for all elements, which results from the ratio of the reference ratio with respect to the instantaneous ratio.

The corresponding formula for the scaling factor results as: Scaling factor steering feel application=(starting ratio reference application)/(instantaneous ratio).

The scaling factor necessary for all modules therefore results as a ratio of the reference ratio with respect to the instantaneous ratio. The instantaneous ratio depends on the different circumstances, such as toothed bar stroke and/or speed of the relevant vehicle. The scaling factor as the result of the ratio formation affects the angle, the angular velocity, and/or the angular acceleration of the steering wheel. The scaling factor can be additionally adapted, for example, to the driving situation or to the driving style of the driver.

FIG. 2 shows a flow chart for the application of a steering feel onto a steering wheel, wherein, in a first step, a reference model is created 7 as a setpoint value of a desired steering feel. This reference model can comprise five units and, in fact, a basic steering torque, an active return, a damping, a hysteresis, and an inertia 8. If it results that the present steering feel, which a driver of the relevant vehicle perceives at the steering wheel, deviates 9 from this desired steering feel, an appropriate adaptation 10 of the steering behavior takes place, in particular of the basic steering torque, the active return, the damping, the hysteresis and/or the inertia, in order to maintain the characteristics of the steering feel.

It is to be noted that the term “includes” does not rule out further elements or method steps, just as the term “a” and “one” does not rule out multiple elements and steps.

The utilized reference numerals are intended merely to enhance the clarity and are not to be considered, in any way, as limiting, wherein the scope of protection of the invention is presented by the claims. 

The invention claimed is: 1-9. (canceled)
 10. A method for adapting a steering feel for a driver of a vehicle at an input element of the vehicle, the vehicle including a steer-by-wire steering system, the method comprising: creating a reference model of the steering feel; selecting scaling factors for the reference model such that at least one of (i) the steering feel and (ii) characteristics of the steering feel remain constant for different steering ratios; and adapting the steering feel using the scaling factors.
 11. The method as claimed in claim 10, the creating the reference further comprising: creating the reference model with components including at least one of (i) a basic steering torque component having as input variables toothed bar force and vehicle speed, (ii) an active return component having as input variables steering wheel angle, driver torque, and vehicle speed, (iii) a damping component having as input variables steering wheel angular velocity, driver torque, and vehicle speed, (iv) a hysteresis component having as input variables steering wheel angular velocity, driver torque, and vehicle speed, and (v) an inertia component having as input variables steering wheel angular acceleration, driver torque, and vehicle speed.
 12. The method as claimed in claim 11, the selecting the scaling factors further comprising: selecting the scaling factors for all components of the reference model based on a ratio of a reference ratio and an instantaneous ratio.
 13. The method as claimed in claim 11, the selecting the scaling factors further comprising: selecting the scaling factors based on at least one of (i) one of a reference basic steering torque and an instantaneous basic steering torque, (ii) one of a reference active return and an instantaneous active return, (iii) one of a reference damping and an instantaneous damping, (iv) one of a reference hysteresis and an instantaneous hysteresis, and (v) one of a reference inertia and an instantaneous inertia.
 14. The method as claimed in claim 13, the adapting the steering feel further comprising: determining a setpoint steering feel as equal to a sum of (i) a product of the basic steering torque component and a first scaling factor of the scaling factors, (ii) a product of the active return component and a second scaling factor of the scaling factors, (iii) a product of the damping component and a third scaling factor of the scaling factors, (iv) a product of the hysteresis component and a fourth scaling factor of the scaling factors, and (v) a product of the inertia component and a fifth scaling factor of the scaling factors.
 15. The method as claimed in claim 14, the selecting the scaling factors further comprising at least one of: determining the first scaling factor as equal to the one of the reference basic steering torque and the instantaneous basic steering torque; determining the second scaling factor as equal to the one of the reference active return and the instantaneous active return; determining the third scaling factor as equal to the one of the reference damping and the instantaneous damping; determining the fourth scaling factor as equal to the one of the reference hysteresis and the instantaneous hysteresis; and determining the fifth scaling factor as equal to the one of the reference inertia and the instantaneous inertia.
 16. The method as claimed in claim 10, wherein the input element is a steering wheel.
 17. A controller for adapting a steering feel for a driver of a vehicle at an input element of the vehicle, the controller being part of a steering system of the vehicle, the controller comprising: a processor configured to: create a reference model of the steering feel; select scaling factors for the reference model such that at least one of (i) the steering feel and (ii) characteristics of the steering feel remain constant for different steering ratios; and adapt the steering feel using the scaling factors.
 18. A steering system for a vehicle, the steering system comprising: a controller configured to adapt a steering feel for a driver of the vehicle at an input element of the vehicle, the controller having a processor configured to: create a reference model of the steering feel; select scaling factors for the reference model such that at least one of (i) the steering feel and (ii) characteristics of the steering feel remain constant for different steering ratios; and adapt the steering feel using the scaling factors.
 19. The steering system as claimed in claim 18, wherein the steering system includes one of (i) a central controller and (ii) a single-wheel controller. 